This invention relates to high density memory devices based on phase change memory materials, including chalcogenide based materials and on other programmable resistance materials, and methods for manufacturing such devices.
Phase change based memory materials, like chalcogenide based materials and similar materials, can be caused to change phase between an amorphous state and a crystalline state by application of electrical current at levels suitable for implementation in integrated circuits. The generally amorphous state is characterized by higher electrical resistivity than the generally crystalline state, which can be readily sensed to indicate data. These properties have generated interest in using programmable resistance material to form nonvolatile memory circuits, which can be read and written with random access.
The change from the amorphous to the crystalline state is generally a lower current operation. The change from crystalline to amorphous, referred to as reset herein, is generally a higher current operation, which includes a short high current density pulse to melt or breakdown the crystalline structure, after which the phase change material cools quickly, quenching the molten phase change material and allowing at least a portion of the phase change material to stabilize in the amorphous state.
The magnitude of the current needed for reset can be reduced by reducing the size of the phase change material element in the cell and/or the contact area between electrodes and the phase change material, so that higher current densities are achieved with small absolute current values through the phase change material.
The size of the phase change element in a memory cell may be reduced by confining it to a narrow volume. In one approach to forming a confined cell structure, a fin-shaped bottom electrode element is formed and then recessed to provide a narrow slot into which the phase change material is deposited. This process presents challenges because it requires that the phase change material fill in a very narrow seam. Moreover, the resulting phase change material fin has a limited height, limiting the power saving performance of the cell.